NANOPARTICLE DISPERSIONS

Abstract

A method for preparing a dispersion of nanoparticles of a solid organic dye or pigment in a liquid carrier, the method comprising forming a solution or slurry of the solid organic dye or pigment in an organic or other solvent, and continuously mixing the solution or slurry with the liquid carrier in a counter current or concurrent mixing reactor providing a dispersion of the nanoparticles in the liquid carrier and solvent mixture and, optionally concentrating the dispersion.

Claims

1. A method for preparing a dispersion of nanoparticles of a solid organic dye or pigment in a liquid carrier, the method comprising i) forming a solution or slurry of the organic dye or pigment in an organic or other solvent, ii) continuously mixing the solution or slurry with the liquid carrier in a counter current or concurrent mixing reactor providing a dispersion of the nanoparticles in the liquid carrier and solvent mixture, and optionally, iii) concentrating the dispersion.

2. A method according to claim 1, wherein one or other of the solution or slurry and the carrier liquid contains a wetting agent and/or a dispersant.

3. A method according to claim 1, further comprising adding a wetting agent and/or a dispersant to the dispersion.

4. A method according to claim 1, wherein the method provides a dispersion of nanoparticles of median (Z) diameter between 100 nm and 300 nm, for example, between 100 nm and 150 nm.

5. A method according to claim 1, wherein the method provides a dispersion having unimodal polydispersity.

6. A method according to claim 1, wherein the method provides a solid content of the dispersion of the solid organic dye or pigment is greater than 5.0 wt/wt % and less than 15 wt/wt % of the dispersion.

7. A method according to claim 1, wherein the method provides a dispersion having a dynamic light scattering (DLS) polydispersity index between 0.1 and 3.0.

8. A method according to claim 1, comprising controlling one or more of nanoparticle size and polydispersity by selection in one or more of the organic or other solvent, the liquid carrier, the temperature and pressure of each of the solution or slurry and the liquid carrier, the residence times of the solution or slurry and the liquid carrier, and the ratio of the flow rates of the solution or slurry and the liquid carrier in the reactor.

9. A method according to claim 1, wherein the liquid carrier comprises water.

10. A method according to claim 9, wherein the organic solvent comprises one or more of ethyl acetate, ethanol, methanol, diethyl ether, tetrahydrofuran, dimethylformamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, acetone, ethylene glycol, propylene glycol and isopropyl alcohol.

11. A method according to claim 1, used for purifying the solid organic compound.

12. A dispersion of nanoparticles of a solid organic dye or pigment in a liquid carrier, obtained or obtainable by the method of claim 1.

13. A dispersion of nanoparticles of a solid organic dye or pigment in a liquid carrier, wherein the nanoparticles consist essentially of the solid organic dye or pigment.

14. A dispersion of nanoparticles of a solid organic dye or pigment in a liquid carrier, wherein the nanoparticles consist essentially of the solid organic dye or pigment and a wetting agent for the nanoparticles.

15. A dispersion according to claim 14, comprising less than 5 wt/wt % of a dispersant.

16. A dispersion according to claim 12, having a solid content of nanoparticles greater than 3 wt/wt % and less than 20 wt/wt %.

17. A dispersion according to claim 12, which has unimodal polydispersity.

18. A dispersion according to claim 12, wherein the nanoparticles have median (Z) diameter between 100 nm and 300 nm, for example, between 100 nm and 150 nm.

19. A dispersion according to claim 12, wherein the liquid carrier comprises water.

20. An ink concentrate for digital inkjet printing, comprising the dispersion of claim 12.

21. A cosmetic paste, comprising the dispersion of claim 12.

Description

[0073] The present invention will now be described in more detail with reference to the following Examples and the accompanying drawings in which:

[0074] FIG. 1 is a schematic illustration of a counter current reactor, described in International Patent Application WO 2005/077505 A2, which is suitable for carrying out the method of the present invention;

[0075] FIG. 2 is graph obtained by dynamic light scattering (DLS) from a dispersion prepared according to an embodiment of one method of the present invention;

[0076] FIG. 3 is a graph obtained by DLS from a dispersion prepared according to another embodiment of the present invention; and

[0077] FIG. 4 is a graph obtained by DLS from a dispersion prepared according to still another embodiment of the present invention.

[0078] Referring now to FIG. 1, a counter current mixing reactor, generally designated 10, comprises a first inlet 11 and an outlet 12 in which a second inlet 13 is diametrically opposed to the first inlet 11 and disposed in the first inlet 11.

[0079] The first inlet 11 and the second inlet 13 are co-axial with one another and the second inlet 12 provides a nozzle 14 in the shape of a conical funnel 15.

[0080] A study of the preparation of several dispersions of nanoparticles of a solid organic dye (Disperse Red 60) in water was undertaken in a counter current mixing reactor as shown in FIG. 1 of laboratory scale.

[0081] The study examined the effect of variation in the ratio of flow rate of solutions of Disperse Red 60 in tetrahydrofuran (THF) with flow rate of water containing a surfactant (Morwet D-425) as wetting agent/dispersant with the ratio of surfactant held constant.

[0082] In a first experiment, a downward flow of water was held at 20 ml/minute and an upward flow of THF solution was varied at values selected between 1 ml/minute and 20 ml/minute. The liquids were pumped by positive displacement pumps and the mixing performed at 25 C. and atmospheric pressure.

[0083] The concentration of the solution (g/L) of dye varied so as to keep the ratio of surfactant to dye constant at 8 whilst the ratio of flow rates varied.

[0084] The resulting dispersions were sampled (see Table 1, A to E) and the samples examined, after concentrating and decanting any sediment, by Dynamic Light Scattering (DLS).

TABLE-US-00001 TABLE 1 Variation of Flow Rates - Surfactant/Dye Ratio 8 Sample Water/THF Surfactant/Dye THF/Dye A 1.00 8.00 500 B 1.33 8.00 375 C 2.00 8.00 250 D 4.00 8.00 125 E 20.00 8.00 25

[0085] The samples were concentrated by rotary evaporation at room temperature (removing THF) followed by rotatory evaporation at 45 until a concentrate having a solid dye loading of about 10 to 15 wt/wt % was obtained.

[0086] The concentrated samples were prepared for examination by dilution of 1 mL of the supernatant fluid in 20 mL of deionised water. The diluted samples were analysed at 25 C. in a 10 mm cuvette using a Malvern Instruments Nano ZS particle sizer fitted with a back-scattering detector at 173 with an incident laser source (HeNe laser with wavelength 632.8 nm).

[0087] A CONTIN algorithm was used to deconvolute the scattered light signal and give a size distribution. The analysis assumed a continuous phase of pure water (viscosity=0.8872 cP; refractive index=1.330) for the measurement settings. The Z-average size of the nanoparticles was taken from the raw cumulants data fit from the DLS instrument.

[0088] FIG. 2 shows the nanoparticle size distribution for two samples B and D of Table 1. As may be seen, the dispersions are unimodal and the Z-average (-median) particle size of the nanoparticles is respectively at 112 nm and 121 nm. The DLS polydispersity index of each sample was determined as 0.131 and 0.189 respectively.

[0089] In a second experiment, the downward flow of water was held at 20 ml/minute and the upward flow of THF solution varied between 1 ml/minute and 20 ml/minute with the ratio of surfactant to dye held constant at 24.

[0090] The liquids were pumped by positive displacement pumps and the mixing performed at 25 C. and atmospheric pressure.

[0091] The dispersion was sampled at different flow ratios (see Table 2, A to E) and the samples were concentrated and examined by Dynamic Light Scattering as described above.

TABLE-US-00002 TABLE 2 Variation of Flow Rates - Surfactant/Dye Ratio 24 Sample Water/THF Surfactant/Dye THF/Dye A 1.00 24.00 500 B 1.33 24.00 375 C 2.00 24.00 250 D 4.00 24.00 125 E 20.00 24.20 25

[0092] FIG. 3 shows the distribution of nanoparticle sizes for samples A and B of Table 2. As may be seen, the dispersions are unimodal and the Z-average (-median) particle size of the nanoparticles are respectively 170 nm and 396 nm. The DLS polydispersity index for each sample A and B was 0.280 and 0.267 respectively.

[0093] The effect of reaction temperature on the size of the nanoparticles was examined by repeating the second experiment in part A at a reaction temperature at 55 C. In this part, the flow ratio of water to THF was 1.00, the concentration of the dye in THF was 2 g/L and the concentration of surfactant in water was 48 g/L. The overall flow rate from the outlet of the reactor was 35 ml/min.

[0094] FIG. 4 shows the distribution of nanoparticle sizes for sample A at this temperature. As may be seen, the dispersion is unimodal and the Z-average (-median) particle size of the nanoparticles is 260 nm. The polydispersity index was 0.218.

[0095] Sample A did not show sedimentation although the other samples showed low but increasing sedimentation in line with decreasing THF content. Increasing the THF content in the mixing beyond that of the present study has been found to eliminate sedimentation and promote complete dispersion of the nanoparticles. All the samples in the study were stable.

[0096] Further studies indicate that stable dispersions of Disperse Red 60 can be obtained using acetone as the solvent without the need for the surfactant.

[0097] These studies taken together clearly show a method providing nanoparticle dispersions of a disperse dye and that the size and polydispersity index of the dispersions are sensitive to, and can be controlled by, the selection of parameters such as ratio of flow rate of the organic solvent with the liquid carrier. Other experiments also show that the method is also sensitive to the selection of organic solvent.

[0098] The present invention provides a single, continuous process for the preparation of stable dispersions of solid organic dye or pigment with desired nanoparticle size and encapsulation of the nanoparticles.

[0099] It also provides a single, continuous process for the purification of solid organic dye or pigment with desired nanoparticle size.

[0100] The present invention enables a large scale and environmentally responsible production of dye or pigment dispersion which generally avoids the large amounts of energy and solvent that are necessary for large scale milling.

[0101] The present invention may allow the preparation of nanoparticle dispersions or nanoparticles of organic dyes or pigments which cannot be milled effectively (for example, Disperse Red 55). It may, therefore, provide access to stable dispersions of solid organic dyes or pigments which are not presently obtainable. It may further provide access to new polymorphs of the crystalline organic dyes or pigments.

[0102] Note that the nanoparticle diameters specified herein are references to diameters which may be determined by, or calculated from, DLS of the dispersions in accordance with ISO 22412:2017. The solid contents specified herein are references to solid contents which may be determined by drying in accordance with ISO 3251:2008.

[0103] Note also that the nanoparticles of the present invention are not comprised by or reliant on an oil-in-water emulsion but are instead comprised by the solid organic dye or pigment or by the solid organic dye or pigment encapsulated (at least in part) by a water soluble surfactant.

[0104] Note further that the methods of the present invention may find general applicability to the preparation of nanoparticle dispersions and nanoparticles of other solid organic compoundsincluding pharmaceutical actives, pharmaceutical additives, pharmaceutical excipients, organometallic dopants or emitters useful in organic light emitting diodes (OLEDs) and organometallic catalysts useful in catalytic convertors and in organic synthesis.